The corals of Queensland's Great Barrier Reef provides divers and snorkellers with a display of colour, shape and movement that is replicated nowhere else in the world. Here are 7 facts to help you understand our underwater world better.

More than 400 (or one-third) of theworld's coral species can be found in the Great Barrier Reef World Heritage Area. Believed to be about 8000-years-old, the thin layer of living coral has built up on top of dead corals and algae over the past 500,000 years.

Hard coral grows up to 1.5cm per year and is the backbone of the reef, growing and constantly adapting to the demands of the environment around it. Formed from a limestone-covered polyp organism dividing into two and leaving behind its hard outer skeleton when a new one is formed.

The reefs exotic coral structures provide a permanent home for a wide range of creatures including a myriad of fish, enchinoderms, molluscs and micro-organisms such as algae and plankton.

Most soft coral species have a symbiotic relationship with microscopic single-celled algae that live inside their tissues, transferring food to the host coral. This very important relationship depends on clear warm shallow waters with temperatures of above 18° C. Dramatic temperature variations can result in the coral expelling the algae, resulting in coral death or coral bleaching.

Coral spawning or reproduction is a nocturnal phenomenon that happens annually in late spring or early summer. Also known as "sex on the reef", egg-engorged corals simultaneously release masses of pretty pink eggs and sperm into the sea to become free-floating larvae. Whilst impossible to predict exactly when it will occur, timing is thought to be related to the water temperature and phases of the moon. It usually occurs with the lunar month about 3-4 days after the full moon. Watch more about Coral Spawning on the Great Barrier Reef.

Apart from climate change and human impact, the reef’s worst natural predator is the Crown of Thornes Starfish. While this species is notorious for stripping reefs of nearly all living coral, fortunately new corals are generally able to re-grow after an outbreak.

Home to a quarter of all known seagrass species, the reef's 500 seaweed and algae species are a significant contribution to the preservation and biodiversity of the reef. They also provide feeding grounds for a number of creatures and form important habitats for dugongs and endangered sea turtles.